Patch "MIPS: Ensure bss section ends on a long-aligned address" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

MIPS: Ensure bss section ends on a long-aligned address

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mips-ensure-bss-section-ends-on-a-long-aligned-address.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Paul Burton <[email protected]>
Date: Mon, 7 Nov 2016 11:52:19 +0000
Subject: MIPS: Ensure bss section ends on a long-aligned address

From: Paul Burton <[email protected]>

[ Upstream commit 3f00f4d8f083bc61005d0a1ef592b149f5c88bbd ]

When clearing the .bss section in kernel_entry we do so using LONG_S instructions, and branch whilst the current write address doesn't equal the end of the .bss section minus the size of a long integer. The .bss section always begins at a long-aligned address and we always increment the write pointer by the size of a long integer - we therefore rely upon the .bss section ending at a long-aligned address. If this is not the case then the long-aligned write address can never be equal to the non-long-aligned end address & we will continue to increment past the end of the .bss section, attempting to zero the rest of memory.

Despite this requirement that .bss end at a long-aligned address we pass 0 as the end alignment requirement to the BSS_SECTION macro and thus don't guarantee any particular alignment, allowing us to hit the error condition described above.

Fix this by instead passing 8 bytes as the end alignment argument to the BSS_SECTION macro, ensuring that the end of the .bss section is always at least long-aligned.

Patchwork: https://patchwork.linux-mips.org/patch/14526/

---
 arch/mips/kernel/vmlinux.lds.S |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -159,7 +159,7 @@ SECTIONS
 	 * Force .bss to 64K alignment so that .bss..swapper_pg_dir
 	 * gets that alignment.	 .sbss should be empty, so there will be
 	 * no holes after __init_end. */
-	BSS_SECTION(0, 0x10000, 0)
+	BSS_SECTION(0, 0x10000, 8)
 
 	_end = . ;
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/mips-irq-stack-unwind-irq-stack-onto-task-stack.patch queue-4.4/mips-ensure-bss-section-ends-on-a-long-aligned-address.patch